1. Field of the Invention
The present invention relates to a swash plate-type, variable displacement compressor for use in a vehicle air conditioning apparatus. More particularly, this invention relates to a swash plate-type, variable displacement compressor that effectively reduces piston top clearance for a range of oblique angles of the swash plate, and thereby reduces the compressor""s vibration, while improving volumetric efficiency.
2. Description of Related Art
In FIG. 1, a known swash plate-type, variable displacement compressor 100 used in a vehicle air conditioning apparatus is shown. The casing of compressor 100 comprises a front housing 101, a cylinder block 102, and a rear housing 103. A drive shaft 104 is provided to pass through the center of front housing 101 and cylinder block 102. Drive shaft 104 is rotatably supported by front housing 101 and cylinder block 102, via bearings 105, 106. In cylinder block 102, a plurality of cylinder bores 107 are arranged equiangularly around an axis 108 of drive shaft 104. In each of cylinder bores 107, a piston 109 is slidably disposed. Pistons 109 reciprocate along a direction parallel to drive shaft axis 108.
A rotor 110 is fixed to drive shaft 104, so that rotor 110 may rotate together with drive shaft 104. Rotor 110 has an arm 110a, through a terminal part of which is provided an oblong hole 110h. Front housing 101 and cylinder block 102 cooperatively define a crank chamber 111. A swash plate 112 having a penetration hole 112c at its center portion is accommodated within crank chamber 111, through which drive shaft 104 penetrates. Penetration hole 112c of swash plate 112 has a complex shape that enables changes of oblique angle of the swash plate 112 with respect to the axis 108. An arm 112a is provided on a front housing side surface of swash plate 112. A pin 112p projects at a terminal part of arm 112a. The terminal part of arm 112a draws a circular locus when arm 112a rotates around axis 108 (i.e., perpendicular to the plane of FIG. 1). Pin 112p projects in a direction tangential to that circular locus. Pin 112p is slidably fitted into oblong hole 110h. Because pin 112p moves within oblong hole 110h, the oblique angle of swash plate 112 with respect to axis 108 varies. Hereinafter, the connection mechanism comprising arm 110a of rotor 110, oblong hole 110h of arm 110a, pin 112p, and arm 112a of swash plate 112, is referred to as C1. The circumferential portion of swash plate 112 has the shape of a planar ring, and is connected slidably to a tail portion of each of pistons 109 via pairs of shoes 113.
When drive shaft 104 is driven by an external power source (not shown), rotor 110 rotates around axis 108 together with drive shaft 104. Swash plate 112 also is made to rotate by rotor 110, via the connection mechanism C1. Simultaneously with the rotation of swash plate 112, the circumferential portion of swash plate 112 exhibits a wobbling motion. A component of movement in the axial direction parallel to axis 108 of the wobbling circumferential portion of swash plate 112 is transferred to pistons 109 via sliding shoes 113. As a result, pistons 109 reciprocate within cylinder bores 107. Finally, in refrigeration circuit operation, a refrigerant may be repeatedly introduced from an external refrigeration circuit (not shown) into a compression chamber 115, which is defined by the piston top of piston 109, cylinder bore 107, and a valve plate 114, to compress the refrigerant by the reciprocation of each piston 109, and to then discharge the refrigerant to the external refrigeration circuit (not shown).
However, such known compressors may exhibit the following limitations. First, in compressor 100, the vertex of the oblique angle is designed to be located at a point 116 at the intersection of a center line 117 of swash plate 112 and axis 108, as shown in FIG. 1. Thus, the position of the vertex of the oblique angle of swash plate 112 depends on the shape of penetration hole 112c of swash plate 112. On the other hand, a center of gravity 118 of swash plate 112 is located at a point relatively far offset above axis 108, as shown in FIG. 1. Because center of gravity 118 of swash plate 112 is relatively far offset from axis 108 of rotation of drive shaft 104, compressor 100 is unbalanced. When drive shaft 104 rotates, this offset generates a vibration in compressor 100. Second, in actual manufacture, connection mechanism C1 may be difficult to make with a low tolerance (i.e., a reduced dimensional variance among the components) because of its complicated shape. As a result, it is difficult to suppress the occurrence of a high tolerance (i.e., increased dimensional variance among the components) between oblong hole 110h and pin 112p. The existence of a high tolerance adversely affects the durability of compressor 100. Third, there may be a problem of controlling piston top clearance. The piston top clearance is a distance between the piston top of piston 109 and valve plate 114 when piston 109 is in a top dead center position.
A need has arisen to reduce compressor vibration, while improving the volumetric efficiency of the compressor. The present invention provides a swash plate-type, compressor having a connection mechanism for the rotor and the swash plate that eliminates or reduces the size of tolerances between compressor components and thereby improves volumetric efficiency. According to the present invention, the compressor may have a connection mechanism between the rotor and the swash plate comprising a link arm having two pivots. This link arm mechanism provides in practice a connection mechanism of the rotor and the swash plate that has a low tolerance. Another need has arisen to locate the vertex of the oblique angle of the swash plate at an improved or optimum position, so that the variation of the piston top clearance as a function of the oblique angle of the swash plate is improved. By making the variation of the piston top clearance as a function of the oblique angle of the swash plate optimum, it is possible to suppress the dead volume and improve the volumetric efficiency of the compressor for the required range of the oblique angle of the swash plate.
In an embodiment of this invention, a swash plate-type compressor includes a front housing, a cylinder block, and a rear housing. A drive shaft is supported rotatably by the front housing and cylinder block. A rotor is fixed to, and rotatable with, the drive shaft. Cylinder bores are arranged around the axis of the drive shaft. Each cylinder bore houses a piston that reciprocates therein. A swash plate is mounted movably on the drive shaft. The pistons are connected to the swash plate by shoes. A connection mechanism links the rotor and swash plate such that the swash plate changes its oblique angle with respect to the drive shaft axis. The connection mechanism includes a first arm that projects from the rotor, a second arm that projects from the swash plate, and a link arm that connects the first and second arms. The first arm and a terminal end of the link arm are connected rotatably by a first pin. The second arm and the other terminal end of the link arm are connected rotatably by a second pin. The first pin extends in a direction tangential to a circular locus formed by a terminal part of the first arm as it rotates around the axis of the drive shaft. The second pin extends in a direction parallel to the first pin.
In another embodiment of this inventions a method is provided for adjusting the location of the vertex of an oblique angle of a swash plate-type compressor. First, a central portion of a swash plate is drilled to form an opening through the central portion of the swash plate. Then, the location of the vertex of the oblique angle is offset from the geometric center of the swash plate by an amount. The swash plate is rotated in a clockwise direction about the offset vertex. Then, a second opening is formed through a central portion of the swash plate.
Other objects, features, and advantages of this invention will be understood from the following description of preferred embodiments with reference to the accompanying drawings.